This application claims the benefit of Korean No. 2001-31452, filed Jun. 5, 2001, in the Korean Industrial Property office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of converting and demodulating a code for source data to be recorded on an optical information storage medium, and more particularly, to a coding and decoding method of more effectively performing a direct current (DC) suppression control of a code stream.
2. Description of the Related Art
In general, an eight to fourteen modulation plus (EFM+) method is a data modulation method used in an optical information storage medium such as a digital versatile disc (DVD). The EFM+ method has a code characteristic of 2, 10, 8, or 16. This indicates that a minimum run length, for example, a minimum length (number) of continuous zeros, of a code stream, is 2 bits, a maximum run length is 10 bits, a length of source data is 8 bits, and a length of a conversion codeword is 16 bits.
FIG. 1 is a block diagram of an example of an EFM+ conversion code group formation. An EFM+ conversion code group includes four main conversion code groups and four corresponding code groups for a DC suppression control. The main conversion code groups are codeword groups into which source data are ordinarily converted. The corresponding code groups for the DC suppression control are codeword groups specially formed to suppress DC components in a code stream, and a codeword of the codeword groups corresponds to a source data item only when a value of the source data item is less than or equal to 87. If the value of the source data item to be converted is less than or equal to 87, a codeword for the source data can be selectively obtained from the corresponding code group for the DC suppression control or the main conversion code group in order to suppress the DC components in the code stream.
As described above, in the conventional EFM+ code modulation method, unless the source data being input (or to be recorded) is less than or equal to a predetermined value (for example, 87), the DC suppression control cannot be performed. That is, the conventional EFM+ method uses a probabilistic method and cannot provide a continuous predictable DC suppression. In this method, it is more disadvantageous that the DC component of the code stream is not sufficiently suppressed in a code having a lower probability of the DC suppression control compared to a code having a higher probability of the DC suppression control. Especially, if the DC component is in a servo band or an RF detection band, a performance of the servo or data detection band may be adversely affected.
To solve the above problems, it is an object of the present invention to provide a code conversion and demodulation method of performing a continuous predictable DC suppression control.
Additional objects and advantageous of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects, according to an embodiment of the present invention, there is provided a codeword conversion method of converting source data into a codeword to be recorded on an optical information storage medium. The method includes inputting the source data, determining whether or not controlling of a direct current (DC) component of a code stream has to be performed, and if a DC control has to be performed, converting the source data into a first codeword based on one of first code groups formed for the DC control, if the DC control is not to be performed, converting the source data into a second codeword corresponding to the source data based on one of second code groups formed according to a format for recording data on the optical information storage medium, determining a code group to be used for converting next source data according to the number of end zeros of the converted codeword, and examining the boundary of codewords of the code stream formed by adding the converted codeword and a previously converted codeword, and if the boundary does not satisfy a predetermined condition, changing the previously converted codeword.
It is possible that a time for the DC control of the code stream is set so that the DC control is cyclically performed for input data.
It is possible that a code group having the number of lead zeros satisfying a predetermined run length condition according to the number of the end zeros of the converted codeword is determined as a code group used for converting the next source data.
It is possible that when the DC control has to be performed, a codeword that is advantageous to suppress the DC component in the code stream is selected from two codeword groups, each group having one codeword of a codeword pair of a plurality of codeword pairs, and the codewords of the codeword pair that have opposite parities and have an identical code group to follow either of the codewords of the codeword pair.
It is possible that when the DC control is not to be performed, a codeword conversion group is selected between a main conversion code group having codewords corresponding to all source data items and an auxiliary conversion code group for the DC control having codewords that have the same length as the codewords of the main conversion code group and is generated to suppress the DC components.
It is possible that the lengths of the codewords of the main conversion code group and auxiliary conversion code group for the DC control are 15 bits long, and the codeword selected when DC control has to be performed is 17 bits long.
Also, to achieve the above and other objects of the present invention, there is provided a code conversion method of controlling a suppression of the DC component contained in the code stream when the source data is converted into a code to be recorded on an optical information storage medium. The method includes determining a control timing for suppressing the DC component of the code stream to which the source data are converted, performing a code conversion at each control time for the DC component so that the code stream branches into a pair of branch code streams one of which extends in a direction where a running digital sum (RDS) of the code stream increases, and another one of which extends in a direction where the RDS of the code stream decreases, and selecting a path of the code stream that has a most bounded path around RDS xe2x80x980xe2x80x99 from paths of the branch code streams branching each control time.
It is possible that in selecting of the path of the code stream from the paths of the plurality of branch code streams, the path of the code stream is selected to have the smallest value obtained when the maximum values of absolute values of respective RDSs of the branch code streams are compared with each other.
It is possible that in selecting of the path of the code stream from the paths of the plurality of the branch code streams, if there are the branch code streams having an identical maximum value (a first step maximum value) in the absolute values of respective RDSs of the branch code streams, one that is not the maximum value of the absolute values of upper and lower limits of the code stream (a second step maximum value) is selected from the absolute values of the upper limit and the lower limit of each code stream, and after comparing the selected values of the branch code streams, the path of a branch code stream having a smaller value is selected.
It is possible that in selecting of the path of the code stream from the paths of the plurality of branch code streams, if there are the branch code streams having an identical first step maximum value and an identical second step maximum value, the sums of absolute values of RDS of respective branch code streams are compared, and a branch code stream having a smaller sum is selected.
It is possible that if there are branch code streams having an identical first step maximum value, an identical second step maximum value, and an identical sum of the absolute values of the RDSs, frequencies of a zero crossing of the RDS values of respective branch code streams are compared and a branch code stream having a highest frequency is selected.
Also, to achieve the above and other objects of the present invention, there is provided a codeword demodulation method of demodulating a codeword read from an optical information storage medium. The method includes reading a codeword, if a DC suppression control is performed in a code conversion, finding a code group corresponding to the read codeword in a pair of first code conversion tables each having one codeword having one of opposite parities, finding source data corresponding to the found codeword, and demodulating the codeword, and if DC suppression control is not performed in code conversion, finding source data corresponding to the read codeword in a second code conversion table.
It is possible that the first code conversion tables and the second code conversion table have 17 bits long codewords and 15 bits long codewords, respectively.
It is possible that the second code conversion table is selected between a main conversion table which has groups classified by the number of end zeros, each group having codewords corresponding to all possible source data, and an auxiliary DC control conversion table which is formed by surplus codewords taken out from the groups of the main conversion table.